During metal processing or simply upon exposure to the atmosphere, a metal oxide layer is often formed over all or part of the metal surface impairing its appearance and/or suitability for further use. One example is steel including particularly mild steel used for fasteners such as screws and bolts. Although the fastener is initially manufactured with a bright, shiny finish, the fastener, upon exposure to the atmosphere, becomes covered wholly or partially with an oxide layer that imparts a dull or blackened appearance. Accordingly, it is desired to remove the metal oxide layer. The conventional way of removing the metal oxide layer is to treat the rusted metal surface with a strong acid such as nitric or sulfuric acid. However, these acids can create environmental problems such as Nox emissions from the use of nitric acid. Also, in the case of fasteners made of mild steel, such strong acid treatments leave the surface with a dull rather than a polished silver-like appearance which is desirable.